1. Field of the Invention
The present invention relates to a porous, preferably dimensionally stable material for the removal of gaseous impurities from a gas mixture, such as H2S, COS, CS2, and SO2, into the pores of which there is incorporated a secondary amine which chemically bonds with the constituents to be removed and a method for such removal.
2. Description of Related Art
The use of porous material incorporating a secondary amine for the removal of gaseous impurities from a gas mixture has earlier been described in GB-A-2 049 468. The porous material described in that document includes mineral carriers which are inert towards secondary amines. Examples of suitable mineral carriers mentioned are pumice, kieselguhr, bauxite, alumina, carbon, and silicates. The particle size preferably is in the range of from 0.1 mm to 5 cm. Further, preference is given to particles having an internal porosity of at least 0.1, for example from 0.1 to 0.8. Internal porosity is defined as the ratio of the volume of internal empty space to the actual volume of the particles of solid; internal porosity is measured for example by means of mercury porosimetry.
In actual practice, using such known materials is attended with a wide range of problems connected with, on the one hand, the presence of minerals in the carrier material and, on the other, the hydrophilic nature of both the carrier material and the employed amines. The presence of traces of certain metals in carrier material of mineral origin may catalyze the conversion of CS2 and COS into sulphur. A drawback to the use of hydrophilic amines is that it leads also to the bonding of CO2. A further drawback consists in that regeneration by means of, e.g, steam stripping, is not readily workable in the case of every gas, for instance in that of CS2.
In accordance with one aspect of the present invention, there is provided a porous, preferably dimensionally stable material for the removal of gaseous impurities from a gas mixture, such as H2S, COS, CS2, and SO2, including a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 xcexcm into the pores of which there is incorporated a secondary amine having hydrophobic properties which chemically bonds with the constituents to be removed.
In accordance with another aspect of the present invention, there is provided a method for the removal of gaseous impurities from a gas mixture including contacting the gas mixture with a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 xcexcm, wherein in the pores thereof there is incorporated a secondary amine having hydrophobic properties which chemically bonds with the constituents to be removed and which optionally is incorporated into a hydrophobic liquid.
These and other objects of the present invention will become apparent upon a review of the following detailed description and the claims appended thereto.
The present invention provides a porous material incorporating in its pores a secondary amine which chemically bonds with the constituents to be removed, which material is easy to regenerate on a commercial scale.
More particularly, the present invention provides a hydrophobic polymer having pores of an average diameter in the range of from 0.1 to 50 xcexcm which contain a secondary amine having hydrophobic properties, which optionally is incorporated into a hydrophobic liquid.
The average pore diameter is determined with advantage using mercury porosimetry in accordance with ASTM D 4284-83.
It is regarded as extremely surprising that the use of a porous material having both a hydrophobic surface area and an average pore diameter in the indicated range provides a system which can be regenerated by means of, e.g., steam stripping and is so effective as to now render industrial scale use possible.
According to the present invention, favorable results are generally obtained when use is made of a porous material where at least 15% of the pores are filled with a liquid composed of secondary amine or a secondary amine-containing liquid.
More preferable results are commonly obtained when use is made of a material where at least 60% of the pores are filled with a liquid composed of secondary amine or a secondary amine-containing liquid.
It has been found that, as a rule, preferable results can be obtained when use is made of a material having an average pore diameter in the range of from 0.2 to 15 xcexcm.
The secondary amines suitable for use according to the invention generally have a low vapor pressure, preference being given to amines having a boiling point of at least 250xc2x0 C. As a rule, favorable results can be obtained when the secondary amine corresponds to the formula R1xe2x80x94NHxe2x80x94R2, wherein R1 represents a functionalized or unfunctionalized (ar)aliphatic group with at least 7 carbon atoms and R2 represents a functionalized or unfunctionalized (ar)alkyl group with at least 3 carbon atoms. Preference is given in this case to secondary amines having a total number of carbon atoms of at least 14. Examples of secondary amines according to the aforementioned formula include dibenzyl amine and ditridecyl amine. Very favorable results are obtained also when use is made of a secondary amine of the formula R3xe2x80x94NHxe2x80x94R4xe2x80x94NHxe2x80x94C(O)Oxe2x80x94R5, wherein R3 represents a functionalized or unfunctionalized (ar)aliphatic group with at least 7 carbon atoms, R4 represents a functionalized or unfunctionalized alkylene group with at least 2 carbon atoms, and R5 represents a substituted or unsubstituted alkyl group with at least 2 carbon atoms. These compounds can be obtained by blocking the primary amino group of a compound having a primary as well as a secondary amino group. As examples of suitable blocking agents may be mentioned ethylene carbonate and propylene carbonate. In the above formula R3 preferably is a coco- or C12 to C14-alkyl group, R4 is an alkylene group with 2 to 6, preferably with 2 or 3 carbon atoms, and R5 is a hydroxyalkyl group with 2 or 3 carbon atoms. Alternatively, it is possible to achieve favorable results by using a secondary amine obtained by converting an alkyl amine with an alkyl(meth)acrylate. As an example of such a compound is the reaction product of oleyl amine and butyl acrylate.
While the hydrophobic secondary amine may be incorporated into the pores of the hydrophobic polymer as such, preference is given to material where the secondary amine is dissolved in a hydrophobic liquid. If a regeneratable absorption system is required, the secondary amine and the hydrophobic liquid preferably both have high thermal, hydrolytic, oxidative, and chemical stability. The glycerol esters of one or more, preferably unsaturated fatty acids may be indicated as examples of a hydrophobic liquid suitable for use according to the present invention, with preference being given to an oil, e.g., palm oil, olive oil, groundnut oil, paraffin oil, fish oil such as herring oil, linseed oil, and, more particularly, soybean oil and/or castor oil. In general, the use of a hydrophobic liquid having one or more tertiary amino groups will be preferred, favorable results are obtained using an alkyl dialkanol amine, more particularly an alkyl diethanol amine, even more particularly a C12 to C14-alkyl diethanol amine. Preferably, the equivalency ratio of secondary amino groups to tertiary amino groups is xe2x89xa61.
The process of preparing from hydrophobic polymers a porous, preferably dimensionally stable material suitable for use according to the present invention has been described, int.al., in U.S. Pat. No. 4,247,498, which is incorporated herein by reference in its entirety. Examples of suitable polymers include: low density polyethylene, high density polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene terpolymers, styreneacrylonitrile copolymers, styrene-butadiene copolymers, polybutene, and poly(4-methyl-pentene-1).
Most preferable results were obtained by using polymers based on polyolefins, with preference being given to the use of a polypropylene based porous material.
Generally, the porous polymer is employed in the form of grains having an average particle diameter of from 0.1 to 10 mm. Alternatively, the polymer may be employed as a granulate and in the form of membranes, fibers which may be hollow or not, and the like. Use in the form of a granulate or powder may be in a packed or fluidized bed. When fibers which may be hollow or not are employed, they are used in the form of fabrics and non-wovens, respectively.
The porous materials filled with secondary amine which, according to the present invention, are suitable for the removal of gaseous impurities may be obtained by filling porous polymers the making of which is described in U.S. Pat. No. 4,247,498, which is incorporated herein by reference in its entirety. However, the preferred preparative process is a variation on one described in GB-A-2 115 425, which is incorporated herein by reference in its entirety, which proceeds as follows: first, from 5 to 90 wt. % of a polymer is dissolved, with heating, at a temperature beyond the critical demixing temperature Tc, in from 10 to 95 wt. % of one or, where necessary, more liquid and miscible compounds A and/or B and/or C, the selected A/B/C mixing ratio being such as will give phase separation on cooling, resulting in a polymer-rich and a polymer-poor phase. On further lowering of the temperature the phase separation structure will be fixed prior to the completion of phase separation due to the polymer vitrifying or crystallizing, resulting in a porous polymer material filled with one or more of compounds A and/or B and/or C and preeminently suited to be used according to the present invention, either as such or after a reduction if so desired. Usually, compound C is added when compounds A and/or B display such a high affinity for the polymer as will result in there not being any liquid/liquid phase separation on cooling prior to vitrification or crystallization.
Up to now, favorable results have been obtained using polypropylene and a mixture of coco- or C12 to C14-alkyl diethanol amine, ditridecyl amine, and the polar triethylene glycol added to prevent the formation, on account of the ditridecyl amine""s strongly apolar character, of a waxy instead of a porous structure on cooling. The pore structure can be affected by adding greater or lesser amounts of triethylene glycol. It has been found the highest absorption capacity for CS2 is obtained when using an equimolar mixture of the secondary ditridecyl amine and the tertiary C12 to C14-alkyl diethanol amine, to which there must further be added about 10 wt. % of triethylene glycol, calculated on the amount of ditridecyl amine and C12 to C14-alkyl diethanol amine.
The invention will be further illustrated with reference to the following specific examples. It is understood that these examples are given by way of illustration and are not meant to limit the disclosure or the claims to follow.